The United States Electric Power Research Institute (EPRI) which is the uniform research facility for domestic electric utilities, predicts that up to 40% of all new generation could be provided by distributed generators by the year 2006. In many parts of the world, the lack of electric infrastructure (transmission and distribution lines) will greatly expedite the commercialization of distributed generation technologies since central plants not only cost more per kilowatt, but also must have expensive infrastructure installed to deliver the product to the consumer.
Relatively small, multi-fuel, modular distributed power generation units commonly called "microturbines" could help alleviate current afternoon brownouts and blackouts prevalent in many parts of the world. Microturbines are a new technology being developed to serve as auxiliary power units, on-site generators, and automotive power plants. Microturbines typically have a maximum power output of about one megawatt. "Turbogenerators" are microturbines, characterized by the following features: (a) a single, integral shaft on which a compressor, turbine and generator are located; (b) the compressor and turbine are of single stage, radial design; (c) the shaft rotates at speeds in excess of 35,000 rpm at full power; (d) an inverter may be used to reduce frequency to typical utility-grade operating parameters, typically 50 or 60 hertz; and (e) a recuperator or regenerator is normally used to bolster efficiency. Both turbogenerators and microturbines can be further characterized as having high power density, compact design and the ability to burn a wide variety of fuels in an external combustor. Some microturbines may be more complex and have features that deviate from the features that characterize a turbogenerator--for instance, they may use multiple shafts, a gear reduction box, and may have an axial flow turbine wheel. Regardless, microturbines may all be characterized in that they are relatively compact gas turbine power generators having no more than one expansion stage, either radial or axial flow, per shaft.
The single moving part concept of a one-shaft microturbine can enable low technical skill maintenance, and the projected low overall cost of such microturbines is expected to allow for widespread purchase in those parts of the world where capital is sparse. In addition, given the United States' emphasis on electric deregulation and the world trend in this direction, consumers of electricity would have not only the right to choose the correct method of electric service but also a new cost effective choice from which to chose. U.S. Pat. No. 4,754,607, which is assigned to the assignee of the present invention, discloses a microturbine power generating system suitable for cogeneration applications.
Yet to make these units commercially attractive to consumers, improvements are needed in areas such as increasing fuel-efficiency, reducing size and weight, and lowering thermal signature, noise, maintenance and cost penalties. For example, increasing the amount of work extracted by the turbine would increase efficiency of the system and lower the cost of generating electrical power.